JPH04502360A - Sensor element for limiting current sensors for measuring the λ value of gas mixtures - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The invention provides a sensor element for a limiting current sensor according to the type of claim 1. It was an idea. This type of sensor element, which operates according to the diffusion-limited current principle, generally The diffusion limiting current is measured with a constant voltage applied to both electrodes of the sensor element. child The current is caused by the expansion of the gas against the pump electrode in the exhaust gas generated during the combustion process. The rate at which the electrode reaction proceeds depends on the oxygen concentration. like this The sensor, which operates according to the polarographic measurement principle, has both an anode and a cathode. exposed to the gas to be measured, the cathode operating in the diffusion-limited current band. It is known to provide a diffusion barrier to achieve this goal.

The known limiting current sensor detects the “total The lambda value of the exhaust gas mixture represents the ratio of oxygen/oxygen required for complete combustion of the power fuel. Commonly used for measurements.

Based on simple and cheap manufacturing methods, ceramic foils and screen printing have recently been used in practice. The value of manufacturing sondes and sensor elements that can be manufactured using technology was recognized.

A simple and reasonably planar polarographic sonde is a flaky or foil-like acid made from an elementary conductive solid electrolyte, such as stabilized zirconium dioxide, and the solid The electrolyte is one of the double-sided pump electrodes (internal or external) and its attached lead plate. covered with. In this case, the internal pump electrode is preferably located in the diffusion slot or in the diffusion channel. at the end, through which the measuring gas can diffuse, and it is a gas diffusion Serves as a resistance.

Furthermore, West German Patent Application No. 3543759 and European Patent Application No. 3543759 Publication No. 0142992, Publication No. 0142993, Publication No. 0188900 and A sensor element and a detector are known from the document No. 0194082; What they all have in common is that they each have a thin or foil-like oxygen-conducting solid material. consisting of a body electrolyte and two above-placed electrodes and one common diffusion Have a pump cell and sensor cell with slits or diffusion passages It is.

Furthermore, DE 38 34 987 A1 describes gas mixtures, in particular Pump installed in an ionically conductive solid electrolyte for the measurement of the λ value of a combustion engine A sensor element for a limiting current type sensor with an electrode pair is described; The pump electrode is connected to the measuring gas through a diffusion slit, and the diffusion slit is connected to the screen. It is coated with a solid electrolyte layer produced using a thin printing technique.

Based on Zr01, which is particularly stabilized by the stacking of a large number of solid electrolyte layers. A disadvantage of known sensor elements manufactured by laminating foils is that the geometry of the diffusion layer is Later modifications, for example for purposes of calibration of ready-made sintered sensor elements, are usually difficult. That's true. In fact, in limiting current sondes, the magnitude of the diffusion current can be determined by various methods. depends on the shape of the diffusion barrier that can be used. This type of diffusion occurs in ceramic sondes. The barrier is advantageously applied by screen printing onto a green ceramic substrate. The whole is then sintered. Only in this way can the limiting current be measured.

In order to eliminate this disadvantage, for example European Patent Publication No. 0191627 From the specifications, it is public to use a sensor element with adjustable resistance in the sensor body. It is knowledge. Still, the disadvantage here is that the manufacturing of such sensor elements is relatively slow. Expensive and expensive and therefore requires additional electrical connections to the sensor body It is to be.

Advantages of the invention The sensor element according to the invention having the advantageous features of claim 1 is disclosed in European Patent Publication No. It is possible to easily manufacture the device known from Japanese Patent Publication No. 0191627. It has the important advantage that it is easy to use and requires few electrical connections. present invention In the case of sensor elements based on The inlet opening of the bath is widened by sequentially corrugating it mechanically or by laser cutting. That is within the range possible. Therefore, the diffused resistance of the fabricated sensor element is advantageous. If it happens that it is too large to be able to operate over a normal load range, then Sections of the tuning band are separated by mechanical means or by laser cutting.

Mechanical cutting of parts of the adjustment band is advantageously carried out by sandblasting or The limiting current is adjusted to a constant value using a ceramic saw, and mechanical processing is used to adjust the limiting current to a constant value. Therefore, the tunnel entrance, for example the tunnel formed by the adjustment zone 8 of the diffusion layer 5 according to FIG. Do this to widen the channel entrance.

When cutting off the adjustment band part by laser cutting, The channel inlet is opened accordingly until a certain limiting current flows.

The geometry of the diffusion layer is adapted to the given conditions of the individual case. This means that the diffusion layer is This means that they can have very different shapes and dimensions.

For example, if it is a square electrode, cover this with a geometrical resemblance, or if it is a circular electrode. This can be wrapped around the electrode field in a circle. Number of tooth profiles, length and distance from each other The separation advantageously depends on the electrode surfaces that can be connected, and the electrode be selected so that it can operate in a favorable load range.

The sensor element according to the invention replaces the known sensor element as a limiting current sensor of conventional construction. Let the server utilize the planar structure. At that time, a broadband sensor [λ≧1 and lean air/fuel A ratio sensor [λ>1] is considered. Thus, the sensor element according to the invention alone, possibly with a heating element, e.g. It can be configured as an air-fuel ratio sensor and as a conventional, e.g. No. 3,206,903 and No. 3,537,051 In cases of lean or rich exhaust gas built into the housing such as It can be used to measure the fuel-air ratio. But also the sensor according to the invention In addition to the pump cell, the sensor element is also equipped with an additional air verification channel. The electrode is located in the pump electrode zone of the diffusion passage of the pump cell and almost The electrode may also have a sensor cell (Nernst cell) located in the air reference passage. Wear.

drawing The drawings show advantageous embodiments of the sensor element according to the invention by way of example.

Individually, they are shown as follows.

FIG. 1 schematically shows a first embodiment of a sensor element according to the invention in a cross-sectional view; Figure 2 shows the shape of the diffusion layer in an overhead track diagram. FIG. 3 schematically shows a second embodiment of a sensor element according to the invention in a sectional view.

Description of examples The sensor element shown diagrammatically in FIG. 1 consists of a ceramic support l, on which a lead An internal pump electrode (cathode) 2 with a lead plate 2' and an external pump electrode with a lead plate 3'. A pump electrode (anode) 3 is supported. The measurement gas is supplied to the internal pump electrode 2. It is introduced via a diffusion slit 6 which is filled with a diffusion layer 4 and a diffusion layer 5 .

The pump electrode 2, lead plate 2' and diffusion layer 5 are covered with an airtight coating layer 7. .

FIG. 2 specifically shows the geometry of the diffusion layer 5 with a tooth-shaped adjustment zone 8. FIG. So The dotted lines represent, for example, zones that can be separated.

The sensor element shown diagrammatically in FIG. 3 consists of a ceramic support 1 and an attached lead plate 2'. an internal pump electrode 2, a diffusion layer 5, a solid electrolyte layer 9, and an attached lead plate 3'. It consists of an external pump electrode 3 having a will be accomplished. The measurement gas introduction takes place at 12. The diffusion layer 5 is also similar to that shown in FIG. It can have a geometrical shape as shown in the example.

The porous diffusion layer 5, which acts as a diffusion barrier, is made from a conventional printing paste. The green ceramic support can be printed using lean printing methods. but It is also possible to print the baked layer on a green support and then sinter the whole thing. Ru. Porous sintered cylinders of corresponding geometry can also be used to form the diffusion layer. can.

The diffusion layer 5 with adjustment zone 8 is preferably made of a coarsely porous sintered material, for example Alto It is composed of a ceramic material based on s or ZrO. In that case, the diffusion layer The porosity is adjusted by the addition of blowing agents that burn, decompose or evaporate during the sintering process. can do. Typical blowing agents that can be used are e.g. black, synthetic resins such as polyurethane-based salts such as ammonium carbonate and and organic substances such as theobromine and indanthrembyl. . The starting material for porous sintering of this type of blowing agent has, for example, a porosity of 10 to 50%. Add in such amount that a substance is produced. Depending on the particle size of the blowing agent used The average diameter that can be determined advantageously lies between approximately 0.1 and 10 μm.

Advantageously, the diffusion layer 5 is further formed in such a way that Knudsen also undergoes vapor phase diffusion. be able to. This means that the diffusion layer forming the diffusion barrier is Knudsen and A channel system for mixed diffusion consisting of gas phase diffusion was developed in West German patent application no. 728289, as described in detail in US Pat. No. 728,289. means.

The ceramic support 1 can be of the type customarily used in the production of sensor elements, for example Z. r　O2 or AI, composed of ceramic materials based on O8, but advantageously The ceramic support 1 is made of a well-known solid electrolyte layer that conducts 02-ions. of tetravalent metals, especially divalent alkaline earth metal oxides and/or or ZrO, Ge01, preferably with a content of oxides of trivalent rare earth elements , Hf　O! and the oxides such as The. Typically the layer from about 50 to 97 mol% from ZrO2, CeO, HfO, or ThO2 and CaO, MgO or SrO and/or rare earth element oxides and special It constitutes 50 to 3 mol% from Y2O2.

In order to manufacture the sensor element, a layer thickness of about 0.5 mm is required in the range of 0.3 to 10 mm. It is advantageous to use foils from sintered ceramic materials as ceramic supports. It turned out that there was.

The pump electrodes 2 and 3 and the associated lead plates 2' and 3' are preferably A metal of white metal, especially platinum, or an alloy of metal of white metal, or gold scrap of white metal. It consists of an alloy with the following metals. In some cases these are ceramic support materials, For example in the form of YSZ powder, the volume component preferably contains about 40% by volume. these are Porous and as thin as possible. Preferably they have a thickness of 8 to 15 μm. Po The lead plates attached to the pump electrodes are also advantageously made of platinum or a platinum alloy of the type mentioned. Composed of gold. Moreover, they are also made of precious metal-cermet based paper. It can be manufactured starting from a stock market.

Organic binder as known paste suitable for printing pump electrodes and lead plates and/or using anti-peeling agents, softeners and organic solvents. Wear. If an insulating intermediate layer is to be manufactured at the same time, the paste may contain pentavalent or is a compound with a higher valence cation, such as a small amount of Nb20s. amount can be added. Examples of anti-peeling additives include Al2os or Z　r　O2 is suitable.

The airtight coating layer 7 is formed by using a layer 7, such as that used to cover electrodes in a flat sensor element. For example, it consists of layers based on AI, O or Mg spinel.

In the case of the embodiment of the sensor element according to the invention shown by way of example in FIG. The electrolyte layer 9 is a known tetravalent electrolyte layer used in the production of a solid electrolyte layer that conducts 02- ions. metals, especially divalent alkaline earth oxides and/or preferably trivalent rare earth elements. such as ZrO2, CeO2, HfO2 and ThO2 with an oxide content of Composed of oxides. Typically the layer comprises up to about 50-97 mole percent ZrO, from CeO2, HfO2 or 'rhos and up to 50-3 mol% Cab, MgO or SrO and/or oxides of rare earth elements and especially Y, 03 or It can be configured from Advantageously, the layer is made of ZrO, stabilized with y,o, Configure from The thickness of the layer is advantageously between 10 and 200 μm, especially between 15 and 50 μm. That's fine.

For the production of the solid electrolyte layer, the paste used is combined with a binder and/or an anti-peeling agent, It can be manufactured using softeners and organic solvents.

Insulating layer 1 that insulates the lead plate 3' of the external pump electrode 3 from the solid electrolyte layer 8 0 to insulate the lead plate from the solid electrolyte when manufacturing flat sensor elements. As normally manufactured, an insulating layer based on AI20s, for example, is constructed. do. The insulating layer 10 may have a thickness of 15 to 20 μm, for example.

In addition, in some cases, such an insulating layer may be applied to the support 1 and the lead plate of the internal pump electrode 2. 2', for example when the support is based on a solid electrolyte. This is the case when the support is a ZrO support.

However, such an arrangement of the insulating layer is not necessarily required.

The glaze 11 is porous and typically used for covering electrodes in flat sensor elements, e.g. For example, it is composed of a layer made of AIto3 or Mg spinel as a paste. Thickness of the shaft is, for example, in the range of 10 to 40 μm.

According to an advantageous embodiment of the invention, the porous glaze is AIs with ZrO2 particles embedded therein of the type known from No. 5.

3 and/or Mg spinel matrix.

Example For the production of a sensor element of the type shown diagrammatically in FIG. 3, a layer thickness of 0. Using foil from zirconium dioxide stabilized with 5 mm . A diffusion layer 5 having the geometrical shape shown in FIG. By means of a screen printing layer from a mixture of ZrO2 of rough particles with a particle size of This brings about thick film technology, in which the theobromine is processed in a temperature range of about 3 in the subsequent sintering process. Evaporate at 00°C. The Zrow solid electrolyte layer 9 is made of Y2 having a particle size of 1 to 2 μm. It is manufactured by printing a paste from ZrO, stabilized with O,. The printed layer is thick It is 80 μm. The attachment of the pump electrodes 2 and 3 made of platinum is likewise known. Made using screen printing technology, the solid electrolyte layer supporting the external pump electrodes 10 μm thick A1. on the surface of the external pump electrode lead plate zone. O, absolute Supports the marginal layer. The pump electrode has a thickness of 12 μm. The lead plate is a normal PT- Starting from cermet paste, 85 parts by weight of Pt powder and 15% by weight of YSZ powder Manufactured from.

To produce the glaze 11, a paste based on Al2O3 is printed. The axis is The thickness is approximately 30 μm.

The covering layer 7 is likewise printed starting from a paste based on AIto.

This had a thickness of about 10 μm.

After coating the electrode, lead plate, insulating layer, glaze and coating layer, the coated support is Subjected to a sintering process, in which it is heated in the region of temperature 1380℃ for a length of about 3 hours be done.

After cutting off the tooth profile of the manufactured sensor element and calibrating it accordingly, a West German patent was issued. It is installed in a housing of the type known from Application No. 3,206,903 and is used for gas mixing. Used to measure the λ value of compounds. Excellent and reproducible test results were thus obtained.

Preferably, the sensor element according to the invention is produced mechanically in multiple printed panels. advantageous The width of the sonde is approximately 4 to 5 mm. The diameter of the electrode is then preferably 3 to 4 mm. 1, for example, 3.6 mm.

---m-1m, PCT/LSI':89100731 International Search Report DE 8900731 SA　32509

Claims (7)

[Claims] 1. External and internal pump voltages placed on one ceramic support and this The internal electrode contains the measuring gas introduced through the diffusion layer, which acts as a diffusion barrier. air covering the diffusion layer as well as the lead plate for the pump electrode. limit voltage for the determination of the λ value of gas mixtures with a dense coating, in particular of the exhaust gases of internal combustion engines. In a sensor element for a flow sensor, a diffusion layer (5) is used for calibration of the sensor element. Limiting current sensor for measuring the λ value of gas mixtures, characterized in that it can be adjusted to sensor element for. 2. The surface of the diffusion layer (5) facing the measurement gas inlet opening is formed into a tooth-shaped adjustment zone. The mechanical or laser cutting part changes the diffusion resistance of the diffusion layer (5). The sensor element according to claim 1, which can be separated while being moved. 3. In the tooth profile adjustment zone (8), the number, length and mutual distance of the tooth profiles are adjusted according to the internal point. The pump electrodes are selected in such a way that they can be operated in an advantageous load range commensurate with the amount of measured gas being diffused. The sensor element according to claim 2, wherein the sensor element is selected from the group consisting of: 4. The diffusion layer 5 may be made of a porous layer based on Al2O3 or ZrO2. The sensor element according to claim 1 or 2. 5. The diffusion layer (5) together with the tooth profile adjustment zone (8) is solid according to screen printing notes. A cell according to any one of claims 1 to 3 printed on the electrolytic support (1). sensor element. 6. The airtight covering layer (7) covering the diffusion layer (5) is made by screen printing technology. The sensor according to any one of claims 1 to 5, comprising a solid electrolyte layer comprising: Sa element. 7. The solid electrolyte support (1) is made of ZrO2 stabilized with Y2O3. The sensor element according to any one of claims 1 to 6.